@wikipedia

Measuring Part of Well & Reservoir Surveillance and one of the Subsurface E&P Disciplines, related to measuring well volumetric flow rate and wellbore pressure in one or few selected wells and interpretation of analysing pressure-rate correlation.

Unlike production analysis which normally covers a time period from few months to many years, well tests are rather short and normally take from few hours to few weeks.

The quantitative interpretation is based on on:

pressure diffusion model

...

with a purpose of dynamic reservoir properties analysis
well completion model with a purpose of Leak Detection

There are different ways to classify the well tests classifications.

One way is to split well tests into two major categories:

Pressure

Testing

Tests	Flowrate

Testing

Tests
DST – Drill Stem Test	SBT – Separator Bulk Test
WFT – Wireline Formation Test	Surface Multiphase Flowmeter
SGS – Static Gradient Survey	Downhole Multiphase Flowmeter
PTA – Pressure Transient Analysis

The other way is to split well tests by data acquisition methodology into three categoriesthe location where the measurements are taken and the well completion status:

Surface

well tests

Well Tests	Subsurface Well Tests
	Open-Hole

well tests

Well Tests	Cased-Hole

well tests

Well Tests
Surface Flowmeter	DST – Drill Stem Test	Downhole Flowmeter
SBT – Separator Bulk Test	WFT – Wireline Formation Test	SGS – Static Gradient Survey
		PTA – Pressure Transient Analysis

Third way is to split well tests by number of wells involved:

Single-Well Tests	Multi-Well Tests

SBT – Separator Bulk Test

Flowrate Testing	PIST – Pressure Interference Step Test (as version of PTA)
SGS – Static Gradient Survey	PICT – Pressure Interference Pulse Test (as version of PTA)
DST – Drill Stem Test
WFT – Wireline Formation Test
Drawdown Test (DD) (as version of PTA)
Injection Test (INS) (as version of PTA)
Build-up Test (BUS) (as version of PTA)
Fall off Test (FOS) (as version of PTA)
MRST – Multirate Step Test (as version of PTA)
SPT – Self-Pulse Test (as version of PTA)